Automatic controls for sewing machines

ABSTRACT

An automatic control means for use in a sewing machine having at least one needle operating to form a line of stitching in response to a workpiece being placed in the position for a stitching operation. More particular, this invention includes a workpiece support plate pivotally mounted on said sewing machine for movement between a upward retracted position and a depressed position. A sensing means is operatively associated with said workpiece support plate for sensing movement of the workpiece support plate to the depressed position. A power drive motor is operatively associated with the sewing machine for effecting operation of the stitching needle. The power drive motor includes a clutch means for moving the power drive means between a nondriving condition and a driving condition. A pneumatic power control cylinder is operatively associated with the clutch means for effecting operation of the clutch means. The pneumatic power control cylinder includes an air supply line operatively connected therewith. An electromagnetic valve means is positioned within said air supply line. The electromagnetic valve means is operatively connected to the workpiece sensing switch whereby operation of the sensing switch will effect energization of the electromagnetic valve means to allow air under pressure to energize the pneumatic control cylinder which will in turn effect operation of the power drive means.

United States Patent Primary Examiner-Jordan Franklin Assistant Examiner-George H. Krizmanich AttorneyNewton, Hopkins and Ormsby ABSTRACTrAn automatic control means for use in a sewing machine having at least one needle operating to form a line of stitching in response to a workpiece being placed in the position for a stitching operation. More particular, this invention includes a workpiece support plate pivotally mounted on said sewing machine for movement between a upward retracted position and a depressed position. A sensing means is operatively associated with said workpiece support plate for sensing movement of the workpiece support plate to the depressed position. A power drive motor is operatively associated with the sewing machine for effecting operation of the stitching needle. The power drive motor includes a clutch means for moving the power drive means between a nondriving condition and a driving condition. A pneumatic power control cylinder is operatively associated with the clutch means for effecting operation of the clutch means. The pneumatic power control cylinder includes an'air supply line operatively connected therewith. An electromagnetic valve means is positioned within said air supplyline. The electromagnetic valve means is operatively connected to the workpiece sensing switch whereby operation of the sensing switch will effect energization of the electromagnetic valve means to allow air under pressure to energize the pneumatic control cylinder which will in turn effect operation of the power drive means.

PATENTED nus I 7 I971 0101/ Mm/cz AUTOMATIC CONTROLS FOR SEWING MACHINES BACKGROUND OF THE INVENTION In the garment industry, a number of sewing machines are used for performing various stitching operations in the manufacture of garments. Each of these sewing machines requires a supply of thread to perform the stitching operation. In the past, all the sewing machines used in the manufacturing of garments included a manually operable control means for effecting operation of the stitching needle. In the use of a manual control means, it was a common practice for the operator to continuously hold the power drive means in a driving condition even after a desired stitching operation had been performed. The continuous running of a sewing machine while not performing a required stitching operation created an excessive amount of waste of the thread material being used by the sewing machine. Over a period of time where a number of sewing machines were in operation, the waste created by the continuous running of the sewing machines-as above stated would accumulate to uncontrollable amounts, which would decrease the efficiency of the garment-manufacturing operation.

Further, in the use of manual control means to effect operation of a sewing machine the operator would become fatigued over a period of time which would in time decrease the operators efficiency in performing her stitching operation.

In the past, numerous attempts have been made to provide automatic control means for effecting operation of a sewing machine. However, the previous automatic control means were complicated in construction, expensive to manufacture, and unreliable in operation.

SUMMARY OF THE INVENTION The abovestated disadvantages of the prior art sewing machine controls is overcome by the present invention which includes specific objects andadvantages as outlined herein below.

It is a primary object of this invention to provide a control means for a sewing machine which is completely automatic in its operation.

It is a further object of this invention to provide an automatic control means for use in a sewing machine having at least one needle operating to perform a line of stitching wherein the control means is operable in response to a workpiece being place in position adjacent the sewing needle for a stitching operation.

It is a still further object of this invention to provide an operable sensing control means supported adjacent a sewing machine stitching needle and used as a workpiece support plate.

A further object of this invention is to provide a workpiece support plate which is supported on a sewing machine adjacent a sewing needle and supported for movement between an upper home position and a depressed position.

Another object of this invention is to provide a workpiece support plate which is adapted to effect operation of a sewing machine and wherein the workpiece support plate is detailed in design to present a substantially smooth surface substantially coplanar with the upper base supporting surface of a sewing machine.

A still further object of this invention is to provide a control means for a sewing machine which includes a pneumatic-controlled cylinder detailed in operation for effecting operation of a power-driven clutch means.

Still another object of this invention is to provide a sensing means for use in the control of a sewing machine which is operable in response to a workpiece being placed in position adjacent a stitching needle and wherein the sensing means is operable with a pneumatic control means for effecting operation of a power drive means.

A still further object of this invention is to provide an automatic control means for use in effecting operation of a series of sewing machines by energization of a common power supply source.

An additional object of this invention is to provide an automatic control means for a sewing machine which is simple in construction, economical to manufacture, and reliable in operation.

Still other objects and advantages of the detail of construction of the illustrative embodiment will become apparent after reading the following description with reference to the accompanying drawings wherein like reference characters have been used to refer to like parts throughout the several figures of drawings.

BRIEF DESCRIPTIONS OF THE FIGURES OF DRAWINGS FIG. 1 is a left front perspective view of a sewing machine utilizing the automatic control means, with certain parts being omitted for purposes of clarity.

FIG. 2 is a front elevational view of the sewing machine shown in FIG. 1, drawn on a larger scale and showing the automatic control means therefore.

FIG. 3 is a fragmentary enlarged sectional view taken substantially along lines 3-3 of FIG. 2.

FIG. 4 is a schematic illustration of the automatic control means associated with a series of sewing machines.

DESCRIPTIONS OF THE ILLUSTRATIVE EMBODIMENT Referring now to the drawing, the sewing machine and control attachment of the illustrative embodiment will be described with reference to a sewing machine 10, a support base 20, a power drive means 40, and automatic control means 50.

As shown in FIGS. 1 and 2, the sewing machine 10 includes a vertically extended main support housing 11 having formed integrally therewith a laterally extended horizontal support portion 12. The support portion 12 includes a vertically reciprocating threading needle 13 which is operable in association with a conventional presser foot 14. It is pointed out that the sewing machine which includes the vertically operable threading needle 13 and the presser foot 14 are of conventional construction and form no part of the present invention.

The sewing machine 10 is supported for operation on a main support base 20, which includes a generally horizontally oriented upper support surface 21. A workpiece support and guide plate 22 is pivotally supported on the main support base 20 adjacent the threading needle 13 and presser foot 14. The workpiece support and guide plate 22 includes an upper surface 23 which is detailed in design and supported in substantially coplanar relationship relative to the upper support surface 21 of the support base 20. The workpiece support plate 22 includes a downwardly sloped toe portion 24 and a rearwardly oriented support heel portion 25. The workpiece guide plate 22 is pivotally supported at 26 to the main support base 20. The pivotal connection 22 includes a threading bolt 27, as shown in FIG. 23, which extends through a compementary opening 28 formed in the heel portion 25. After the threaded bolt 27 passes through the opening 28, the extended end of bolt 27 passes through a heel support bracket 29 with a threaded nut 30 connected thereto. It is pointed out that the workpiece support plate 28 and guide surface means 22 is detailed in design to be supported adjacent the needle 13 and presser foot 14 whereby an operator placing a workpiece in position to be stitched, will rest the workpiece support plate 22. The pivotal connection including the threaded bolt 27 and complementary opening 28 is detailed to allow the support plate 22 to be pivoted downwardly from a position which is coplanar with the upper support surface of the support base 20 to a depressed position below the upper support surface. As shown in FIG. 3, the heel support bracket 29 will cooperate with the support plate heel portion 25 and threaded connection 27 to permit limited pivotal movement of the support plate 22.

Referring now particularly to FIG. 2, the sewing machine includes a power drive means 40, for effecting operation of the stitching needle 13. The power drive means 40 includes a conventional electric motor 41. A conventional clutch means 42 is operatively associated with the drive motor for effecting movement of the power drive means from a nondriving condition to a driving condition. A clutch control arm 43 is pivotally supported at 44 on the clutch housing 42. Extending laterally outward from the clutch control housing 42 is a drive shaft 45. Fixed to the drive shaft 45 is a driving pulley 46 a power drive is delivered to the sewing machine 10 by means of a belt 47 which is in driving engagement with a pulley 48. The pulley 48 is fixed to the sewing machine power control shaft 49. The above-described sewing machine power drive means is of conventional construction and it is obvious that by operating the clutch mechanism 42 to move the power drive means to a driving condition, rotary power will be delivered by the pulleys 46, 48 and belt 47 to the sewing machine foreffecting a stitching operation of the needle 13.

As shown in Fig. 2 and 3, the sewing machine 10 includes an automatic control means 50 for effecting operation of the power drive means 40. The automatic control means includes a sensing switch 51 which is supported beneath the toe portion 24 of the workpiece support plate 22. The switch means 51 includes a threaded housing or body portion 52 and an operable plunger means 53. A compression spring 54 is supported around the switch 51 and plunger 53 and between the workpiece support plate 22 and the base support portion 20. The amount of spring-biasing force on the support plate 22 is adjustable by a threaded retainer element 55 which is supported on the threaded portion 52 of the switch 51. The sensing switch 51 is electrically connected to a solenoid 57 by means of leadlines 56. Solenoid 57 is operatively associated with a conventional pneumatic control value 58. The control valve 58 has a pneumatic supply input line 59 and an output supply line 60. The output supply line 60 is connected to a pneumatic cylinder 61. The cylinder 61 is of conventional construction and includes a piston rod 62 which has its extended end pivotally connected at 63 to the clutch control arm 43. A compression spring is supported around the piston rod 62 and held thereon by means of a retainer 65. The retainer 65 is connected to the piston rod 62. The cylinder 61 and spring means 64 are detailed such that the spring will maintain the clutch control arm 43 in a position which'will shift the drive motor to a nondriving condition when the pneumatic cylinder is not energized.

The above-described association of the sensing switch 51, the electromagnetic solenoid 57, valve 58, and pneumatic control cylinder 61 are detailed in operative association relative to each other such that movement of the workpiece support plate 22 to a depressed position will effect operation of the sensing switch 51 which will in turn energize the solenoid 57, opening the valve 58, to allow a supply of air under pressure to be delivered to the control cylinder 61. Energization of the control cylinder 61 will effect movement of the clutch control arm 43 to shift the clutch 42 to a driving condition for effecting operation of the stitching needle 13.

Referring now particularly to FIG. 4, an electrical and pneumatic control means is shown for operation ofa series of scwing machines which are supported adjacent each other. As shown in Flg. 4, each of the sewing machines includes a workpiece support plate 22, which is operatively associated with a sensing switch 51. The sensing switch is electrically connected to a conventional electromagnetic solenoid 57 which is operatively associated with a conventional valve means 58. Each valve means 58 is connected to an air supply source and includes an output supply line which is operatively associated with a pneumatic control cylinder 61 for effecting operation of sewing machine controls, as stated hereinabove.

OPERATIONS To begin a stitching operation with the sewing machine 10 an operator will first move a manually controlled switch (not line of stitching on the garment, as desired. As an operator positions a workpiece on the workpiece support plate 22, the toe portion 24 of workpiece support plate 22 will be pressed downwardly by the weight of the workpiece and the operators hands to close the sensing switch 51. After the sensing switch 51 has been closed, electrical power will be allowed to flow along the leadlines 56 to energize the solenoid 57. Energization of the solenoid 57 will effect a movement of the valve structure (not shown) to an open position to allow a supply of air under pressure to be delivered along the output supply line 60 to the pneumatic control cylinder 61. Introduction of a supply of air into the cylinder 61 will effect a movement of the piston rod 62 leftward, as shown in Flg. 2, to effect an operation of the clutch 42. Operation of the clutch 42 will effect a movement of the drive motor 41 to a driving condition which will in turn, deliver rotary power through the pulley 46, belt 47, and pulley 48, to the sewing machine 10 for effecting operation of the stitching needle 13.

After a garment has been stitched, and the operator has allowed the workpiece support plate 22 to return to an upward retracted home position by means of the compression spring 28, the electrical power will be discontinued to the solenoid 57. The deenergization of the solenoid 57 will close the valve 58, which will in turn, shut off the supply of air under pressure to the control cylinder 61. After the supply of air has been discontinued to the control cylinder 61, the compression spring 64 will return the clutch control arm 43 to a neutral position to disengage the drive motor or return the drive motor to a nondriving condition. It is to be noted that the pneumatic control cylinder 61 includes a conventional airescape means (not shown) which will allow the air under pressure in the cylinder to escape therefrom as the spring 64 returns the piston rods and clutch control arm to a neutral position.

The operation of a series of sewing machines as illustrated in the schematic diagram of FIG. 4 would occur substantially as described above in the description of a single sewing machine.

It now becomes apparent that the above-described illustrative embodiment of an automatic sewing machine control is capable of obtaining the above-stated objects and advantages. It is obvious to those skilled in the art that modifications may be made in the details of construction without departing from the spirit of the invention which is to be limited only by the scope of the appended claims.

What I claim is:

1. In an automatic control means for use in a sewing machine having at least one needle operating to form a line of stitching, said automatic control means comprising, in combination:

a. power drive means operatively associated with said sewing machine for movement between a nondriving condition and a driving condition whereby said power drive means effects operation of said stitching needle;

b. clutch means supported on said sewing machine and operatively associated with said power drive means for effecting movement of said power drive means between said nondriving condition and said driving condition;

c. pneumatic control means operatively associated with said clutch means for effecting operatively associated with said clutch means for effecting operation of said clutch means to move the power drive means to said driving conditions;

d. A workpiece support plate supported on said sewing machine adjacent said stitching needle, said workpiece support plate being supported for movement between an upward retracted position and a depressed position in workpiece support plate and said pneumatic control I means, and wherein movement of said support plate to said depressed condition will effect operation of said pneumatic control means, whereby the clutch means will effect movement of the power drive means to a driving condition for operation of said stitching needle.

2. In an automatic control means for use in a sewing machine as was described in claim 1 further characterized in that said sensing control means includes an electrically operable switch means supported beneath said workpiece and electrically connected to an electromagnetic control valve operatively associated with said pneumatic control means.

3. In an automatic control means for use in a sewing machine as described in claim 2 further characterized in that said switch means includes spring-biasing means for urging said workpiece support plate upwardly to said home position.

4. In an automatic control means for use in a sewing machine as described in claim 3 further characterized in that said switch and spring-biasing means includes an adjustable means operatively associated therewith whereby the springbiasing force of said spring means can be varied.

5. In an automatic control means for use in a sewing machine as described in claim 1 further characterized in that said workpiece support plate includes an upper workpiece engaging surface which is supported in substantially coplanar alignment with the upper surface of said sewing machine base support.

6. In an automatic control means for use in a sewing machine as described in claim 5 further characterized in that said workpiece support plate includes a forwardly extending toe portion and a rearwardly extending heel portion and wherein said workpiece heel portion is pivotally connected to said support base for permitting pivotal movement of said support plate to said depressed position about a substantially horizontal transverse axis.

7. ln an automatic control means for use in a sewing machine as described in claim 6 further characterized in that said pivotal connection for connecting said heel portion of said workpiece support plate includes a vertically extending threaded connecting bolt passing through a complimentary opening in said heel portion and wherein said threaded connecting bolt and complementary opening are detailed in adjustment to permit movement of said workpiece support plate toe portion to a depressed position in response to a workpiece being positioned thereon for a stitching operation.

8. In an automatic control means for use in controlling a series of sewing machines wherein each of said sewing machines includes at least one needle operating to form a line of stitching, said automatic control means for said series of sewing machines comprises, in combination:

a. a power drive means operatively associated with each of said sewing machines and detail for movement between a nondriving condition and a driving condition wherein said power drive means effects the operation of said stitching needle when in said driving condition;

b. a workpiece support plate supported on each of said sewing machines adjacent said stitching needle, each of said workpiece support plates being detail for movement from an upward retracted position to a depressed position in response to an operator placing a workpiece in position to be stitched by said stitching needle;

. pneumatic control means operatively associated with each of said sewing machine power drive means for effecting movement of said power drive means to said driving condition;

d. sensing means operatively associated with each of said sewing machines workpiece support plates for sensing movement of said workpiece support plate to said depressed position, said sensing means being operatively associated with said pneumatic control means and detail in design for effecting operation of said pneumatic control means in response to a workpiece being positioned at a stitching position.

9. In an automatic control means for use in a series of sewing machines as described in claim 8 further characterized in that said power drive means includes a clutch means operatively associated with said power drive means and said pneumatic control means, said clutch means being detail in design for movement of the power drive means to a driving condition in response to energization of said pneumatic control means, and wherein said pneumatic control means includes means for returning said clutch control means to said nondriving condition in response to deenergization of said pneumatic control means.

10. In an automatic control means for use in a series of sewing machines as described in claim 8 further characterized in that said control means includes a pneumatic cylinder operatively associated with each of said sewing machine power drive means, a common air supply means operatively associated with all of said pneumatic control means and a electromagnetic valve means operatively associated with each of said pneumatic control cylinders, said electromagnetic control valve includes means operatively associated with said sewing machine sensing means for effecting energization of said electromagnetic means in response to movement of said workpiece support plate to said depressed position.

11. In an automatic control means for use in a sewing machine having at least one needle operating to form a line of stitching, said automatic control means comprising, in combination:

a. power drive means operatively associated with said sewing machine, said power drive means detailed in design for movement between a nondriving condition and a driving condition whereby said power drive means willeffect operation of said stitching needle when moved to said drive condition;

b. a workpiece support plate supported on said sewing machine adjacent said stitching needle, said workpiece support plate being supported for movement between an upward retracted position and a depressed position in response to a workpiece being positioned adjacent said stitching needle for a stitching operation; and,

. sensing control means operatively associated with said workpiece support plate and operatively associated with said power drive means for effecting movement of said power drive means to said driving condition in response to movement of said workpiece support plate to said depressed position.

12. In an automatic control means for use in a sewing machine as described in claim 11 further characterized in that said workpiece support plate includes a forwardly extending toe portion and a rearwardly extending heel portion, said workpiece support plate being pivotally connected adjacent said heel portion and detailed in design whereby said workpiece support plate toe portion is moved to a depressed position in response to a work piece being positioned adjacent said stitching needle for a'stitching operation.

13. In an automatic control means for use in a sewing machine as described in claim 12 further characterized in that said workpiece support plate includes an upper supporting surface, said workpiece support plate being detail in supporting relationship relative to a sewing machine support base whereby said workpiece upper surface is substantially coplanar with the upper supporting surface of the sewing machine support base.

14. in an automatic control. means for use in a sewing machine as described in claim 11 further characterized in that said sensing control means and a electrically operable switch means and wherein said switch means is positioned adjacent said workpiece support plate for sensing movement of said workpiece work plate to said depressed position, said switch means being detailed for effecting operation of said electromagnetic valve means, and wherein the operation of said electromagnetic valve means is detailed to effect operation of said pneumatic power control cylinder. 

1. In an automatic control means for use in a sewing machine having at least one needle operating to form a line of stitching, said automatic control means comprising, in combination: a. power drive means operatively associated with said sewing machine for movement between a nondriving condition and a driving condition whereby said power drive means effects operation of said stitching needle; b. clutch means supported on said sewing machine and operatively associated with said power drive means for effecting movement of said power drive means between said nondriving condition and said driving condition; c. pneumatic control means operatively associated with said clutch means for effecting operatively associated with said clutch means for effecting operation of said clutch means to move the power drive means to said driving conditions; d. A workpiece support plate supported on said sewing machine adjacent said stitching needle, said workpiece support plate being supported for movement between an upward retracted position and a depressed position in response to a workpiece being positioned adjacent said stitching needle for a stitching operation; e. a sensing control means operatively associated with said workpiece support plate and said pneumatic control means, and wherein movement of said support plate to said depressed condition will effect operation of said pneumatic control means, whereby the clutch means will effect movement of the power drive means to a driving condition for operation of said stitching needle.
 2. In an automatic control means for use in a sewing machine as was described in claim 1 further characterized in that said sensing control means includes an electrically operable switch means supported beneath said workpiece and electrically connected to an electromagnetic control valve operatively associated with said pneumatic control means.
 3. In an automatic control means for use in a sewing machine as described in claim 2 further characterized in that said switch means includes spring-biasing means for urging said workpiece support plate upwardly to said home position.
 4. In an automatic control means for use in a sewing machine as described in claim 3 further characterized in that said switch and spring-biasing means includes an adjustable means operatively associated therewith whereby the spring-biasing force of said spring means can be varied.
 5. In an automatic control means for use in a sewing machine as described in claim 1 further characterized in that said workpiece support plate includes an upper workpiece engaging surface which is supported in substantially coplanar alignment with the upper surface of said sewing machine base support.
 6. In an automatic control means for use in a sewing machine as described in claim 5 further characterized in that said workpiece support plate includes a forwardly extending toe portion and a rearwardly extending heel portion and wherein said workpiece heel portion is pivotally connected to said support base for permitting pivotal movement of said support plate to said depressed position about a substantially horizontal transverse axis.
 7. In an automatic control means for use in a sewing machine as described in claim 6 further characterized in that said pivotal connection for connecting said heel portion of said workpiece Support plate includes a vertically extending threaded connecting bolt passing through a complimentary opening in said heel portion and wherein said threaded connecting bolt and complementary opening are detailed in adjustment to permit movement of said workpiece support plate toe portion to a depressed position in response to a workpiece being positioned thereon for a stitching operation.
 8. In an automatic control means for use in controlling a series of sewing machines wherein each of said sewing machines includes at least one needle operating to form a line of stitching, said automatic control means for said series of sewing machines comprises, in combination: a. a power drive means operatively associated with each of said sewing machines and detail for movement between a nondriving condition and a driving condition wherein said power drive means effects the operation of said stitching needle when in said driving condition; b. a workpiece support plate supported on each of said sewing machines adjacent said stitching needle, each of said workpiece support plates being detail for movement from an upward retracted position to a depressed position in response to an operator placing a workpiece in position to be stitched by said stitching needle; c. pneumatic control means operatively associated with each of said sewing machine power drive means for effecting movement of said power drive means to said driving condition; d. sensing means operatively associated with each of said sewing machines workpiece support plates for sensing movement of said workpiece support plate to said depressed position, said sensing means being operatively associated with said pneumatic control means and detail in design for effecting operation of said pneumatic control means in response to a workpiece being positioned at a stitching position.
 9. In an automatic control means for use in a series of sewing machines as described in claim 8 further characterized in that said power drive means includes a clutch means operatively associated with said power drive means and said pneumatic control means, said clutch means being detail in design for movement of the power drive means to a driving condition in response to energization of said pneumatic control means, and wherein said pneumatic control means includes means for returning said clutch control means to said nondriving condition in response to deenergization of said pneumatic control means.
 10. In an automatic control means for use in a series of sewing machines as described in claim 8 further characterized in that said control means includes a pneumatic cylinder operatively associated with each of said sewing machine power drive means, a common air supply means operatively associated with all of said pneumatic control means and a electromagnetic valve means operatively associated with each of said pneumatic control cylinders, said electromagnetic control valve includes means operatively associated with said sewing machine sensing means for effecting energization of said electromagnetic means in response to movement of said workpiece support plate to said depressed position.
 11. In an automatic control means for use in a sewing machine having at least one needle operating to form a line of stitching, said automatic control means comprising, in combination: a. power drive means operatively associated with said sewing machine, said power drive means detailed in design for movement between a nondriving condition and a driving condition whereby said power drive means will effect operation of said stitching needle when moved to said drive condition; b. a workpiece support plate supported on said sewing machine adjacent said stitching needle, said workpiece support plate being supported for movement between an upward retracted position and a depressed position in response to a workpiece being positioned adjacent said stitching needle for a stitching operation; and, c. sensing control means operatively associAted with said workpiece support plate and operatively associated with said power drive means for effecting movement of said power drive means to said driving condition in response to movement of said workpiece support plate to said depressed position.
 12. In an automatic control means for use in a sewing machine as described in claim 11 further characterized in that said workpiece support plate includes a forwardly extending toe portion and a rearwardly extending heel portion, said workpiece support plate being pivotally connected adjacent said heel portion and detailed in design whereby said workpiece support plate toe portion is moved to a depressed position in response to a work piece being positioned adjacent said stitching needle for a stitching operation.
 13. In an automatic control means for use in a sewing machine as described in claim 12 further characterized in that said workpiece support plate includes an upper supporting surface, said workpiece support plate being detail in supporting relationship relative to a sewing machine support base whereby said workpiece upper surface is substantially coplanar with the upper supporting surface of the sewing machine support base.
 14. In an automatic control means for use in a sewing machine as described in claim 11 further characterized in that said sensing control means and a electrically operable switch means and wherein said switch means is positioned adjacent said workpiece support plate for sensing movement of said workpiece work plate to said depressed position, said switch means being detailed for effecting operation of said electromagnetic valve means, and wherein the operation of said electromagnetic valve means is detailed to effect operation of said pneumatic power control cylinder. 